The present invention has been developed to lessen the incidence of bronchopulmonary dysplasia (BPD, a chronic lung problem found in premature infants) caused by mechanical ventilation. Although not conclusively proven, pulmonary barotrauma due to mechanical ventilation is thought to be an important etiological factor in BPD.
The present invention allows accurate determination of increases in pulmonary dynamic compliance. These increases permit decreases in the mean airway pressure to be made during mechanical ventilation. Decreasing mechanical ventilation pressure reduces the incidence and severity of pulmonary barotrauma.
An exhaustive search of the prior art disclosed several patents which pertained to the construction or production of devices that utilize an hydraulic medium with an endotracheal tube. Issued to Baum in 1985, U.S. Pat. No. 4,535,766 discloses a method and apparatus for monitoring a respirator in use with an endotracheal tube. The pressure of the respiratory gas source is controlled through a pneumatic link with a measuring tube which terminates at or near the distal end of the endotracheal tube. Baum also teaches an open hydraulic system and indicates that water (the fluid) emitted by a jet nozzle serves to humidify the respiratory gas. The invention's purpose in using a liquid fluid, therefore, is to humidify and not to monitor intrapulmonary pressure. This is a state of the art employment of an hydraulic fillen lumen within a standard endotracheal tube.
Issued to Jackson, U.S. Pat. No. 3,854,484, discloses a closed hydraulic system within close proximity of the endotracheal tube. The Jackson device, instead of using air to fill the occlusive cuff of an endotracheal tube, uses a liquid medium. Jackson discloses no other purpose for the closed hydraulic system than sealing the area between the endotracheal tube and esophogeal wall.
The present methods of dynamic monitoring of intrapulmonary pressures include central venous pressure, transpulmonary (esophageal) and distal pneumatic catheterization. These three modes of monitoring suffer limited accuracy due to: (1) indirect measurement of pneumobarometic pressure, because the target pressure area is beyond the placement of the intratracheal artificial airway; (2) the influence of the non-airway artifact on the intrapulmonary pressure; and (3) external (ambient) air pressure influence upon an open transducing system.
It is therefore the object of this invention to provide a new intrapulmonary monitoring device which does not rely upon these three modes and therefore avoids their disadvantageous aspects. This is accomplished by: (1) locating the sensor proximate the pulmonary region to be measured; (2) positioning the sensor near the exterior, distal end of the endotracheal tube, thus eliminating the artifact effect of turbulent air flow; and (3) utilizing a closed hydraulic sensor-transmitter system, eliminating the problems relating to an open system, namely, avoiding errors due to air compression by using an incompressible fluid.